1. Field of the Invention
The present invention relates to a magnetic head including a light source, for writing signals by using heat-assisted magnetic recording, and to a method for manufacturing the magnetic head.
2. Description of the Related Art
As the recording density of a magnetic recording and reproducing apparatus, represented by a magnetic disk apparatus, becomes higher, further improvement has been required in the performance of a thin-film magnetic head. As the thin-film magnetic head, a composite-type thin-film magnetic head is widely used, which has a stacked structure of a magnetoresistive (MR) element for reading data and an electromagnetic transducer for writing data.
A magnetic recording medium, on the other hand, generally is magnetically discontinuous, in which magnetic microparticles are gathered together. Usually, each of the magnetic microparticles has a single magnetic-domain structure, and in the medium, one record bit consists of a plurality of the magnetic microparticles. Therefore, for improving its recording density, irregularity in the boundary of the record bit is required to be reduced by decreasing the size (volume) of the magnetic microparticle. However, a problem is likely to occur that the decrease in size causes thermal stability of the magnetization of the record bit to be degraded.
As a measure against the thermal stability problem, it may be possible to increase the magnetic anisotropy energy KU of the magnetic microparticles. However, the increase in energy KU causes the increase in anisotropic magnetic field (coercive force) of the magnetic recording medium. Whereas, write field intensity of the thin-film magnetic head is limited by the amount of saturation magnetic flux density of the soft-magnetic pole material of which the magnetic core of the head is formed. Therefore, the head cannot write data to the magnetic recording medium when the coercive force of the medium exceeds the write field limit.
Currently, as a method for solving the thermal stability problem, heat-assisted magnetic recording technique is proposed, in which a magnetic head writes data to the magnetic recording medium formed of a material originally having large magnetic anisotropy energy KU, by reducing the anisotropic magnetic field of the medium with heat supplied to the medium just before the write field is applied. As proposed heat-assisted magnetic recording techniques, U.S. Pat. No. 6,768,556 describes a near-field light probe for irradiating light to the recording medium, which has a metal scatterer with a strobilus shape formed on a substrate and a dielectric material film formed around the metal scatterer. And US Patent Publication No. 2004/081031 A1 describes a scatterer as a near-field light probe, which is formed in contact with the main magnetic pole of a single-pole-type head for perpendicular magnetic recording in such a way that the irradiated surface of the scatterer is perpendicular to the medium surface. Furthermore, Miyanishi et al. “Near-field Assisted Magnetic Recording” IEEE TRANSACTIONS ON MAGNETICS, Vol. 41, No. 10, p.2817-2821 (2005) describes a U-shaped near-field light probe formed on a quartz crystal slider.
As described above, various forms of heat-assisted magnetic recording techniques are proposed. However, the present inventors suggest a heat-assisted magnetic recording head constituted by joining a light source unit provided with a light source to the end surface (back surface) opposite to the opposed-to-medium surface of a slider provided with a write head element. For example, US Patent Publication No. 2008/043360 A1 discloses such a light source unit. The advantages of the just-described heat-assisted magnetic recording head are as follows:
a) The head has an affinity with the conventional manufacturing method of thin-film magnetic heads because the opposed-to-medium surface and the element-integration surface are perpendicular to each other in the slider.
b) The light source can avoid suffering mechanical shock directly during operation because the light source is provided far from the opposed-to-medium surface.
c) The light source such as a laser diode and the head elements can be evaluated independently of each other; thus the degradation of manufacturing yield for obtaining the whole head can be avoided. Whereas, in the case that all the light source and head elements are provided within the slider, the manufacturing yield rate for obtaining the whole head is likely to decrease significantly due to the multiplication of the process yield for the light-source and the process yield for the head elements.
d) The head can be manufactured with reduced man-hour and at low cost, because of no need to provide the head with optical components such as a lens or prism which are required to have much high accuracy, or with optical elements having a special structure for connecting optical fibers or the like.
Manufacturing such a heat-assisted magnetic recording head requires a higher accuracy of alignment when joining the light source to the back surface of the slider. In fact, the present inventors have adopted a structure in which a waveguide is provided within a slider to guide light from a light source to the opposed-to-medium surface through the waveguide. When joining a light source unit to such a slider, the light-emission center of the light source needs to be made accurately coincide with the incident center of the waveguide located on the back surface of the slider in order to obtain sufficient light use efficiency. In practice, the accuracy required of the alignment is within +/−1 μm both in the waveguide-width direction (Y-axis direction, which will be described later) and the waveguide-thickness direction (Z-axis direction, which will be also described later).
If a laser diode is used as the light source, the outer surface of the laser diode on the opposite side to the adhered surface of the laser diode serves as one reference for the alignment between the light-emission center and the incident center. The light-emission center is at a position in an active layer between the n-electrode and p-electrode of the laser diode. The active layer is a predetermined distance apart from each of the n-electrode and the p-electrode. Accordingly, in both cases where the n-electrode is adhered and the p-electrode is exposed as the outer surface and where the p-electrode is adhered and the n-electrode is exposed as the outer surface, it is difficult to accurately recognize the location of the light-emission center in the alignment between the light source unit and the slider. Consequently, it is considerably difficult to achieve alignment in two directions (Y-axis and Z-axis directions, which will be described later) in the back surface of the slider, which may be likely to reduce the efficiency of mass-production of the head.